Method of forming a plunger for a check valve

ABSTRACT

A plunger for a check valve and a method for constructing such a plunger. The preferred plunger has a shell of P.T.F.E. sealingly secured to a rigid, metal disk. The cavity betwen the shell and the disk is filled with a silicone rubber material which, together with the shell, provides a resiliency that enables the shell to conform to irregularities in its mating valve seat even when the seating pressure is low. The shell preferably has an outwardly bowed, tapered sidewall for providing a circumferential line contact with a frustoconical valve seat. In accordance with the method, the shell begins as a sheet that is hot molded around the pre-formed rubber silicone, and the outer edge of the shell is inserted into a groove in the disk to envelope the filler material. The outer diameter of the disk is reduced to sealingly capture the shell edge, thereby forming a unitary structure.

This is a divisional of co-pending application Ser. No. 037,687 filed on04/13/87.

BACKGROUND OF THE INVENTION

The present invention relates to flow control devices and, particularly,to valves of the type generally known as "soft" seated check valves.More specifically, this invention is directed to enhancing theperformance of check valves, especially at low back pressure and incorrosive environments, and to a method of fabricating a corrosionresistant check valve characterized by such enhanced performance.

Soft seated check valves are generally of two types, ball cone andtapered plug. Although conventional valves of these types can beeffective in checking the reverse flow of fluid though a line, theirperformance under low back pressure has often been unsatisfactory. Theball in the ball type valve is porous, and the mounting and operatingcharacteristics are somewhat complicated, so that such valves are noteasy to repair while in line. The tapered plug valves are typically ofsimpler design and more readily accessible for repair, but these types,even when new, have difficulty providing a good seal at low backpressure.

An exemplary prior art tapered plug check valve is disclosed in U.S.Pat. No. 3,677,286, in which a valve chamber is located between an inletchannel and an outlet channel, and a valve seat is located between theinlet channel and the valve chamber. A valve plug or plunger issupported in registration with the valve seat for engagement thereofwhen the fluid pressure in the chamber exceeds the pressure in the inletchannel. The sealing effect is accomplished by the mating of two taperedsurfaces in a wedge-like action. At low seating pressure, the wedge-typeinteraction between the valve seat is applied over a relatively largecontact area and a full circumferential seal cannot be assured. At veryhigh back seating pressure, the molded valve seat disclosed in thereferenced patent is subject to being pushed through the passagewaybetween the chamber and the inlet channel, thereby destroying the sealand resulting in valve failure.

SUMMARY OF THE INVENTION

The present invention overcomes the above-mentioned and otherdeficiencies in conventional soft seated check valves, by the use of acomposite valve plunger or plug which interacts with the valve seat in amanner that achieves satisfactory sealing over a wide range of reverseflow pressures.

In one embodiment, the invention is directed to a valve having a bodyportion including an inlet channel, an outlet channel and a chamberfluidly connected therebetween, with a valve seat and associated flowpassage located between the inlet channel and the chamber. The valveseat has an upper, flat rim portion and an inwardly tapered portionextending from the flat rim into the flow passage. A valve member havinga composite head or plunger is supported so as to establish, in theclosed position and even at low back pressure, a line contact sealbetween the front portion of the plunger and the tapered portion of thevalve seat. This line contact seal results from the shape and materialproperties of the plunger.

The plunger includes a thin frontal shell of a corrosion resistant,pliable material such as polytetraflorethylene ("Teflon"), hereinafterP.T.F.E., the shell being secured to a metal backing disk. The cavityformed between the hollow shell and the disk is filled with a relativelysofter, resilient material such as silicone rubber. The shell sidewallsare preferably radiused as by the arc of a sphere or parabola toproduced a slightly outwardly bowed profile such that initial contactbetween the shell and the tapered valve seat will be substantially acircumferential line contact, rather than a wedge-type circumferentialsurface contact. Particularly at low backseating pressures, theavailable sealing force is more effectively utilized in achieving theintegrity of a line contact. The equivalent total force is dissipatedover a larger surface in conventional tapered plug valves. Preferably,the disk portion of the plunger has an outer diameter sufficient toregister with the flat rim portion of the valve seat and thereby preventthe plunger from blowing through the passageway at very high backpressures.

In the method embodiment of the invention, the plunger is constructed byforming a shell having a closed front and arcuate side portions, theshell including a generally circular projection at its rear portion. Theshell is filled with a relatively softer, more resilient material, and ahard metal backing disk with a circular groove is force fit into tightengagement with the projections on the shell. This isolates the fillermaterial from the environment and, preferably, provides a firm backingsurface for the filler material.

The combination of a very soft plunger head and a rugged but smooth"Teflon" seating area insures reliable sealing junction with the valveseat. The design of the plunger head radius and the cooperating seatangle allow the plunger head to develop a continuous line contact withseat, thereby maximizing the effect of what little pressure may beavailable to push the plunger head against the seat insuring a goodseal. As pressure builds, the plunger head is forced further into theseat until disk rests on top of the web in the valve body which definesthe seat area, thus preventing further deformation of the plunger headand preventing blow through. The resiliency of the plunger allows thehead to return to its proper shape when the plunger lifts off the seatduring flow cycling. The plunger will crack open at minimal pressurebecause no real wedging action between the plunger and the seat occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

The above-discusses and other objects and advantages of the inventionmay be better understood by reference to the accompanying description ofthe preferred embodiment and drawings, in which:

FIG. 1 is a section view of a check valve in accordance with the presentinvention;

FIG. 2 is a side view of the valve plunger shown in FIG. 1;

FIG. 3 is an enlarged detail of the valve seat area of the valve shownin FIG. 1;

FIG. 4 is a section view of the valve plunger taken, along lines 4--4 ofFIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows a check valve 10 according to the present invention havinga generally "y" shaped body portion 12 defining an inlet channel 14horizontally aligned with an outlet channel 16. A valve chamber 18fluidly connects the channels 14 and 16, the chamber being orientedvertically obliquely relative to the horizontal. A valve seat structure20 is formed in a body web portion between the inlet channel 14 and thechamber 18. A valve member 22 is supported in the chamber 18 forreciprocal movement toward and away from the valve seat 20. The valveseat 20 defines a flow passage 24 connecting the inlet channel 14 andthe chamber 18. Upon the occurrence of a higher pressure in the chamber18 than that in the inlet channel 14, the valve will be closed by theplunging action of the valve member 22 against the seat 20.

The valve member 22 includes a head portion 26 and a stem 28. The stemextends into a bore 30 formed in the valve cap 32. Valve cap 32 engagesthreads 34 formed the upper portion of the chamber 18. Preferably, aboss 36 is formed as an extension of the bore 30, such that a coilspring 38 can be interposed between the valve head 26 and the cap 32 toincrease the responsiveness of the checking action of the valve when theparticular nature of the service conditions so demands. The cap 32preferable has an hexagonal portion 40 to facilitate the threading ofthe cap into the chamber, and a gasket 42 is preferable provided betweenthe flange 44 of the cap and a seat or groove whereby the process fluidwithin the valve is prevented from leaking into the environment.

FIG. 2 illustrates the preferred shape of the valve head 26. The headhas a leading plunger portion including a closed front portion 48 andarcuate side portion 50 for engaging the valve seat. The side portion 50is radiused as shown at 52 to form an outwardly bowed profile. Theplunger portion is backed by a metal disk 54. When viewed in thedirection of flow the head is circular.

FIG. 3 shows the details of the preferred valve seat 20, including aflat rim portion 56 forming a part of the floor of the chamber 18 and aninwardly tapered portion 60 leading to the inlet channel 14. Thepreferred embodiment of a one inch check valve would have a 15 degreetapered angle 62 extending between a major outer diameter 64 of about1.058 inches to the 1.000 inch diameter 66 of the inlet flow channelpassage 24. The valve seat may also be formed by a molded insert (notshown) of P.T.F.E. or the like located in an undercut portion of thebody between the chamber and inlet channel. With reference also to FIG.2, the preferred valve head 26 for use with the valve seat 20 of the oneinch valve shown in FIG. 3, would have a side wall radius of curvature52 of about 0.553 inch extending between a major diameter 68 of about1.060 inch and a minor diameter 70 of about 0.949 inch. The diameter 70of the disk portion 54 would preferably be about 1.220 inches.

FIG. 4 is an exploded section view of the valve member 22. Thecomponents include a stem 28 which, in the disclosed embodiment,threadily engages a blind hold formed in the circular disk 54, both ofwhich are preferable made from 316 stainless steel, as is the valvebody. The stem may also be affixed to the disk by staking. The plungernose is made of a P.T.F.E. molded shell 72 which is preferable made fromthin Teflon (between 0.010-0.020 inch), further having a thickened,rearwardly projecting annular lip 74 and a radially projecting rim 76. Apre-formed silicone rubber button 78 having a hardness in the range ofabout 10-30 durometer, preferably about 20 durometer, is located withinthe cavity of the hollow shell 72 in intimate engagement with the front48 and sidewalls 50 thereof. The mating surface 80 of the disk 54 ispreferable sandblasted or etched, and the mating surface 82 of thesilicone button 78 will be coated with a suitable adhesive forattachment to the disk during the final assembly of the plunger.Preferably, either one or both of the front portion 85 of the siliconebutton 78 and the inside surface of the "Teflon" shell is etched.

Preferably, the shell 72 is formed by heat molding a sheet of "Teflon"over the silicone button 78. The shell 72 is joined to the disk 54 byforcing the lip 74 into a circular groove 84 on the disk. Any excessmaterial resulting from the molding of the shell into the disk caneasily be trimmed. The disk outer diameter is then cold headed, crimpingthe lip 74 inside the groove 84, thus sealing the silicone button fromcontact with the fluid in the operating environment. Accordingly, thevalve of the present invention is suitable for use in corrosiveenvironments.

The construction of the valve member should be carefully controlled tomaintain the dimensional relationships and plunger profile such thatcontact between the plunger and the valve seat occurs when the disk isbetween about 0.030 and 0.070 inch above the valve seat rim 56 (see FIG.3). The initial line contact established at this elevation within thevalve seat will seal against back flow at minimum back pressure becausethe back pressure is applied against a thin line contact thus creatingmore force against the seat over less area than if the contact werespread out over a large area as would occur with a frustoconical valveseat and complementary shaped plunger. The flexible nature of thesilicone allows the plunger to seal even against minor imperfections inthe seating area. As back pressure builds the plunger is forced downinto the seat a short way until the overhanging disk contacts the rim 58of the valve seat. This allows the check valve to withstand considerablepressure without deforming the plunger nose or "blowing through" theseat. To achieve the desired result, the relationship of the plungerradius, seat angle, seat thickness, and manufacturing tolerances must becontrolled. Preferably, these dimensions and tolerances are taken withrespect to the inlet channel diameter. Valve seat tolerance should bekept between plus or minus one degree, and preferably plus one-halfdegree minus zero degree, and the plunger radius tolerance should bemaintained within about plus 0.0 minus 0.005 inch.

The composite valve plunger described above is preferably employed withthe y-type valve body, wherein the chamber is oriented at an angle ofbetween 45 and 60 degrees relative to the inlet channel, and the valvecap is removable to allow access to the seat area and to the plunger forcleaning or replacing components without disconnecting the inlet andoutlet channels from the proces line.

While a preferred embodiment has been shown and described, variousmodifications and substitutions may be made thereto without departingfrom the spirit and scope of the invention. Accordingly, it is to beunderstood that the present invention has been described by way ofillustration and not limitation.

What is claimed is:
 1. A method of forming a plunger for a valvecomprising the steps of:providing a rigid metal disk with a front andback surface and a circular groove on said front surface; forming abutton from a material having a durometer rating in the range of 20-30,said button including front and back surfaces and a side wall extendingtherebetween, said front and back surfaces being generally parallel andcoaxial and said front surface being smaller in area than said backsurface; forming a shell comprising a material having a low coefficientof friction around said button, said shell being in part complementaryin shape to said button, being in intimate contact with the frontsurface and side wall of said button and having an annular lip; andisolating said button from the ambient environment by forcing saidannular lip into said circular groove to thereby encapsulate said buttonbetween said shell and said disk; and attaching a stem to said backsurface.
 2. The method of claim 1 wherein the step of isolating saidbutton includes compressing the disk to sealingly capture the lip insaid circular groove.
 3. The method of claim 1 wherein said button isadhesively joined to said disk.
 4. The method of claim 3 wherein saidbutton is adhesively joined to said disk and thereafter the shellmaterial is hot molded over said button and secured to said disk.